Number of the Day: 52.2
52.2 -- the average cost in the US, in cents per mile, of driving a car alone, according to AAA. Compare that to...
20.7 -- the average cost in the US, in cents per mile, of riding public transportation, according to the American Public Transportation Association.
Of course, these numbers take into account myriad assumptions and factors that don't apply to everyone (more explanation is available from the links above) and aren't meant to be absolute; just an interesting comparison and perhaps something you didn't already know. Learn more with TreeHugger's How to Green Your Public Transportation and How to Green Your Car Guides.